The invention relates to an inductive measuring arrangement for coin validation in free-fall coin-operated devices according to claim 1.
In many conventional coin validators, an inserted coin runs along a descending coin chute and during its path is validated by appropriate sensors for its authenticity. There are extensive prior art documents relating to this subject. The advantage of a coin moving along a coin chute when the measuring is carried out is that the coins have a predetermined position relative to the sensors. As a result, the spacing of the coins from the sensors is not particularly important. A drawback with such coin-operated devices is, however, that the coins are moved relatively slowly through the coin-operated device and in this manner restrict the frequency of insertion.
Free-fall coin-operated devices have become known from EP 0839364, the entire contents of which is incorporated herein by reference, in which the inserted coins fall downwards as a result of gravitational force and are validated for authenticity by sensors assigned to the drop path. The specification for the sensors is particularly high, as the coins fall relatively rapidly through the measuring channel and the position of the coins relative to the sensors fluctuates.
Inductive measuring probes preferably consist of a transmitting coil and a receiving coil, which are arranged on both sides of a coin channel. During this inductive measurement, a distinction is made between a transmissive measurement and a reflexive measurement. During transmissive measurement, the field of the transmitting coil passes through a coin. From the attenuation of the field, the receiving coil measures at least one specific parameter of the coin. During reflexive measurement, the transmitting and receiving coils are located on one side of the free-fall path. This measurement detects the surface and/or the region close to the surface of the coins as, for example, specific outer layers. From DE 10 2004 013 286, the entire contents of which is incorporated herein by reference, a coil arrangement has already become known in which the transmitting coil is wound onto an elongate ferrite core, and the receiving coil of smaller diameter is arranged recessed on the front face of the magnetic core in a recess. The core permits a relatively uniform magnetic field, and the receiving coil is substantially decoupled from the transmitting field. As a result, it is possible to undertake a reflexive coin measurement by means of the inductive probe, irrespective of the spacing of the coin. If a further receiving coil is arranged on the opposing side of the coin path, a transmissive measurement may be undertaken by means of the known coil arrangement. The arrangement is advantageous for use in multifrequency technology, in which a plurality of harmonics of the alternating magnetic field of the transmitting coil are examined for their effect on the coins.